Many methods of bleaching teeth and their effects on the surrounding tissues and pulp have been reported. The effect of bleaching agents on the enamel surface has received some investigation, but the products selected for the present study have not been included in previous scanning electron microscopic studies. In vitro scanning electron microscopic evaluation revealeld that the enamel surf ace underwent considerable changes after 1 hour of exposure to one of four bleaching agents. These changes increased in direct relation to the length of time that the enamel surface was exposed to the oxygenation (bleaching) agent.